[Jorg]

Hi everyone. Someone mentioned in the amplification Forum that it's easy to make a balanced amp from two regular. Is it true and how can one implement it? Search gave me no results. Please help me with this, thanks!

 

[amb]

Yeah, it's basically two stereo amplifiers, each operating in "bridged" mode. The second amplifier in each channel must have its phase reversed, and you must modify the headphone cable so that it's no longer a 3-wire setup. The two sides must have separate pairs, and these are connected across the outputs of the two amplifier on each side. Under ideal conditions, you get four times the output power in this configuration.

See the project library at headwize.com on the Kevin Gilmore dynamic amp, it has some description about how it's done for that amp.

-Ti

 

[Jorg]

Thanks, amb! But how can I get the phase reversed?

 

[dip16amp]

If you have a balanced source like the Benchmark DAC1, there are two ways to connect them.

The first way is to have one amp for positive left and positive right and the second amp for negative left and negative right. Also connect the ground wire from each amp to the source. Then make an output cable that connects the positive left and negative left to the left earpiece and the positive right and negative right to the right earpiece. The DAC1 volume control can adjust the balanced output, so each amp volume can be set for maximum. Normal unbalanced headphones can still be plugged on each amp for unbalanced mode without changing the input cables.

The other way is to have one amp for positive left, negative left, and ground and the other amp for positive right, negative right, and ground. Then make an output cable from each amp to each earpiece. This way would have better stereo separation.

 

[amb]

Quote:

Originally Posted by Jorg Thanks, amb! But how can I get the phase reversed?

Aside from having a balanced source (such as the DAC example above), there are a couple of different ways to invert the phase for the second amp on each side.

One way is to make that second amp work in a phase inverting mode, and derive its input signal from the first amp. This involves some fundamental changes to signal routing within the amp and how negative feedback is applied. There are variations on the details of how this is done, depending on amp topology (e.g., whether the amp is opamp-based or all-discrete, etc). The Gilmore balanced dynamic amp is a classic example of this in a discrete amp.

Another way is to add a phase inverter circuit before the input to the second amp. This has the drawback of extra complexity (another active stage is needed) and additional noise, distortion, high frequency phase shifts, etc...

Unfortunately, details about these techniques could span a chapter in an electronics textbook, and is not something that could be easily explained in a posting like this. If you are using a pair of amps that were not originally made to run in balanced mode, and you wish to modify it, you should have someone who has the technical skills and knowhow to do it.

Note that each amp in a bridged pair "sees" only half of the load impedance, so if you're using low-Z phones this may be problematic. Improperly implemented bridging of the two amps could also lead to circuit instability (oscillations).

-Ti

 

[Sennator]

Hi all!
I have an sacd-player with balanced output. I ask myself if a balanced headphone amp makes sense. Can anybody explain, why it sounds better? The studio standard is made for long cables we don't have at home....

When I connected the balanced output to my unbalanced headphone amp I had a better resolution and more details... Any eplaination?

 

[Jorg]

Quote:

Originally Posted by Sennator Hi all! I have an sacd-player with balanced output. I ask myself if a balanced headphone amp makes sense. Can anybody explain, why it sounds better? The studio standard is made for long cables we don't have at home.... When I connected the balanced output to my unbalanced headphone amp I had a better resolution and more details... Any eplaination?

You may want to read the Blockhead manual on www.headphone.com . There is no point in retelling it here.

And another comment from Dr. Gilmore:
http://www6.head-fi.org/forums/showp...5&postcount=16

But to answer your question: Yes, there is point in balanced amplification, especially for Grados.

 

[comabereni]

.

 

[vanillawafer]

Quote:

Originally Posted by Jorg You may want to read the Blockhead manual on www.headphone.com . There is no point in retelling it here. And another comment from Dr. Gilmore: http://www6.head-fi.org/forums/showp...5&postcount=16 But to answer your question: Yes, there is point in balanced amplification, especially for Grados.

YIKES! That is one expensive amp! So I guess the best way to take advantage of the E-MU 1212m balanced outs is to buy one of those bad boys and also modify your headphones, from what I gather even if you had balanced in's on your amp paired with balanced out's on the source you would not get the benefit of a balanced system because the head phones are not balanced, am I correct in my assumption?

 

[drewd]

Quote:

Originally Posted by vanillawafer YIKES! That is one expensive amp! So I guess the best way to take advantage of the E-MU 1212m balanced outs is to buy one of those bad boys and also modify your headphones, from what I gather even if you had balanced in's on your amp paired with balanced out's on the source you would not get the benefit of a balanced system because the head phones are not balanced, am I correct in my assumption?

Well, you wouldn't derive the full benefit of balanced operation, but certainly the source and amplifier would benefit from increased slew rates and noise rejection. The degree of benefit depends on where the amplifier does the conversion from balanced to single ended operation, though. Balanced headphones would give you that last bit of sonic nirvana, but even as single ended devices, you'll hear a difference through your headphones with balanced cables between the source and amplifier.

-Drew